Hybrid dysegenisis is a syndrome of associated aberrant traits in Drosophila melanogaster which occurs non-reciprocally in the F1 hybrid progeny of crosses between certain strains. The sydrome includes high mutation rates, sterility, male recombination, distorted transmission ratios, chromosomal aberrations, non-disjunction and local increases in female recombination. Complex interstrain interactions are involved in the etiology of hybrid dysgenesis and environmental factors also have a critical effect on its manifestation. The potential for hybrid dysgenesis is wide spread in both natural and laboratory populations throughout the world. The objective of current research is to investigate the etiology and mode of inheritance of one system of hybrid dysgenesis. Emphasis is placed on determining the nature and mode of transmission of the two interacting components, i.e. the chromosomally linked "factors" and the cytoplasmic component. The transposability of the chromosomal factors is being investigated including various factors affecting the frequency of this phenomenon. The role of environmental factors, such as temperature and age, in affecting the wide quantitative variation in dysgenic traits is also of considerable interest.